This invention relates to process and apparatus for continuously anodizing aluminum. The term aluminum is used herein to include aluminum base alloys which, like pure aluminum, can be electrolytically anodized to form oxide coatings. More particularly, this invention relates to a technique for continuously anodizing coils or lengths of aluminum, such as aluminum sheets, strips, wire, rods, shapes and the like (hereinafter collectively referred to as aluminum web).
Aluminum in sheet, strip and wire form has been continuously anodized by a number of techniques for many years. See, for example, U.S. Pat. Nos. 3,865,700, issued Feb. 11, 1975 and Re. 29,754, reissue Sept. 5, 1978. Such anodized products used for electrical and decorative purposes, in the manufacture of household appliances, automotive trim, building materials, farm equipment, furniture, sporting goods, cans, container closures, lithographic plates, transformers, and in many other market and product areas.
Because anodizing forms an aluminum oxide coating which is a dielectric, current introduced into the web for anodizing is carried in the web after anodizing. This is manifested by undesirable arcing when the edges of the web contact the sides of subsequent treatment tanks or the coil is sheared.